1. Field of the Invention
The present invention relates to a method and apparatus for producing laminated iron cores each having a predetermined skew amount by stacking iron core sheets while performing a skewing operation.
2. Description of the Prior Art
A laminated iron core used in a rotor or the like for an electric motor is usually formed therein with oblique or skew slots for the purpose of improving its electrical characteristics. In order to make such slots, it is necessary to sequentially shift respective slot holes formed in each iron core sheet. To this end, a metallic mold apparatus for manufacturing this types of laminated iron cores has a so-called skewing function, for example, as disclosed in U.S. Pat. No. 3,110,831.
However, in such a conventional mold apparatus having the skewing function, the thickness of the laminated iron core (sometimes referred to as a product, hereinafter), that is, the total thickness of the laminated core sheets is controlled according to the number of such core sheets. Therefore the apparatus has a disadvantage that, when the thickness of the core sheet changes, the thickness of the resultant product correspondingly changes. Such a disadvantage can be prevented by using the total thickness of laminated sheets in place of the number of such laminated core sheets to control the thickness of a product. However, in this case, there unfavorably takes place variations in the skew angle of the product for the following reason.
That is, in such a conventional apparatus, each time a piece of iron core sheet is piled on the uppermost sheet, the skewing operation is effected by a constant skew angle (for example, 0.1.degree.-0.2.degree.) and therefore the skew amount (the skew of the product depends on the number of laminated iron core sheets because the skew amount is expressed by angle times the number of laminated iron core sheets. As a result, when the thickness of the iron core sheet changes and correspondingly the number of laminated core sheets varies from product to product, the skew angle varies depending on these products.